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#include "codeeditor.h"

#include <QPainter>
#include <QTextBlock>

CodeEditor::CodeEditor(QWidget *parent) : QPlainTextEdit(parent)
{
    lineNumberArea = new LineNumberArea(this);

    // 每当按下回车或者删除回车(更新字符块),则newBlockCount计数,并触发该信号, newBlockCount 默认为1
    connect(this, &CodeEditor::blockCountChanged, this, &CodeEditor::updateLineNumberAreaWidth);
    // 每当光标的位置发生变化时，触发该信号
    connect(this, &CodeEditor::updateRequest, this, &CodeEditor::updateLineNumberArea);
    // 当内容变化时, 触发该信号
    connect(this, &CodeEditor::cursorPositionChanged, this, &CodeEditor::highlightCurrentLine);

    // 更新行号区域, 默认情况下块的数量是0
    updateLineNumberAreaWidth(0);
    // 高亮当前行
    highlightCurrentLine();
}


int CodeEditor::lineNumberAreaWidth()
{
    // 计算行号区域有多少位数字
    int digits = 1;
    int max = qMax(1, blockCount());
    while (max >= 10) {
        max /= 10;
        ++digits;
    }

    // 计算宽度 3 + 字符宽度 * 行号数字位数
    // 参考:
    // QFontMetrics : https://blog.csdn.net/kenfan1647/article/details/115171891
    int space = 3 + fontMetrics().horizontalAdvance(QLatin1Char('9')) * digits;

    return space;
}


void CodeEditor::updateLineNumberAreaWidth(int /* newBlockCount */)
{
    setViewportMargins(lineNumberAreaWidth(), 0, 0, 0);
}


void CodeEditor::updateLineNumberArea(const QRect &rect, int dy)
{
    if (dy)
        lineNumberArea->scroll(0, dy);
    else
        lineNumberArea->update(0, rect.y(), lineNumberArea->width(), rect.height());

    if (rect.contains(viewport()->rect()))
        updateLineNumberAreaWidth(0);
}


void CodeEditor::resizeEvent(QResizeEvent *e)
{
    QPlainTextEdit::resizeEvent(e);

    QRect cr = contentsRect();
    lineNumberArea->setGeometry(QRect(cr.left(), cr.top(), lineNumberAreaWidth(), cr.height()));
}


void CodeEditor::highlightCurrentLine()
{
    QList<QTextEdit::ExtraSelection> extraSelections;

    if (!isReadOnly()) {
        QTextEdit::ExtraSelection selection;

        QColor lineColor = QColor(Qt::yellow).lighter(160);

        selection.format.setBackground(lineColor);
        selection.format.setProperty(QTextFormat::FullWidthSelection, true);
        selection.cursor = textCursor();
        selection.cursor.clearSelection();
        extraSelections.append(selection);
    }

    setExtraSelections(extraSelections);
}

void CodeEditor::lineNumberAreaPaintEvent(QPaintEvent *event)
{
    QPainter painter(lineNumberArea);

    // 1. 填充背景
    painter.fillRect(event->rect(), Qt::lightGray);

    // 2.计算行号区域的头和底的坐标(头设置为原点)
    QTextBlock block = firstVisibleBlock(); // 当前页面, 第一块可见的文本区域
    int blockNumber = block.blockNumber(); // 第一块可见的文本区域的块编号，(编号从0开始，所以最开始是0)

    // 3.保证绘画的起始行号的头和文本块的头平齐
    // qRound: 四舍五入
    // blockBoundingGeometry(block):  返回块的矩形，这里的块的顶部坐标为0；
    // QRectF QRectF::translated(const QPointF &offset) const:
    //                  返回对进行偏移offset的矩形,这里的块的顶部坐标为内容偏移的坐标；
    int top = qRound(blockBoundingGeometry(block).translated(contentOffset()).top());
    int bottom = top + qRound(blockBoundingRect(block).height());

    // 如果块有效，(用回车键分配了)
    while (block.isValid() && top <= event->rect().bottom()) {

        // 块可见，底部坐标大于当前事件的顶部坐标
        if (block.isVisible() && bottom >= event->rect().top()) {
            // 因为块呈序列的，从0开始，所以可以将块号+1，作为行号
            QString number = QString::number(blockNumber + 1);
            painter.setPen(Qt::black);
            painter.drawText(0, top, lineNumberArea->width(), fontMetrics().height(),
                             Qt::AlignRight, number);
        }

        block = block.next();
        top = bottom;
        bottom = top + qRound(blockBoundingRect(block).height());
        ++blockNumber;
    }
}

